1. Field of the Invention
The present invention relates to a wireless communication apparatus, a wireless communication method, a computer program, and a wireless communication system. Specifically, for example, the invention relates to a wireless communication apparatus, which performs communication using a millimeter wave by directing the beam of the directional antenna to the direction of the communication target location, a wireless communication method therefor, a computer program therefor, and a wireless communication system using the same.
2. Description of the Related Art
In wireless communication, there have been developments in technologies of millimeter-wave communication for promoting utility, such as large-volume and long-distance transmission, a decrease in size of wireless equipment, and reduction in cost, and which have been mainly used for short distance wireless access communication, image transmission systems, simple wireless communication, anti-collision radars for vehicles, and the like. The wavelength of the millimeter wave is in the range of 1 mm to 10 mm, which corresponds to 30 GHz to 300 GHz in terms of frequency. For example, in the wireless communication using a 60 GHz band, it is possible to allocate a channel in units of GHz, and it is also possible to perform high-speed data communication.
The millimeter wave has a short wavelength and excellent straightness, and enables transmission of very large volume of information, as compared with the microwave having come into widespread use in the wireless LAN (Local Area Network) technology. In contrast, since the millimeter wave is rapidly attenuated in accordance with reflection, the direct wave thereof or the just one-time reflected wave is mainly used as a path of the wireless communication. In addition, since the millimeter wave has a large propagation loss, the millimeter wave has a property that the wireless signal does not reach far.
To complement the problem in the reach distance of the millimeter wave, a method is conceivable in which directivity is provided to the antenna of the transceiver and the communication distance is increased by directing the transmission beam and reception beam of the antenna to the direction of the communication target location. The directivity of the beam can be controlled, for example, in a way that a plurality of antennas are respectively provided to the transceivers and the weighting of transmission or the weighting of reception is changed for each antenna. In the millimeter wave, the reflected wave is scarcely used, and thus the direct wave becomes important. From this point, it is conceivable to use a directional beam which is pointed. In addition, the optimal directivity of the antenna is learned, and then the millimeter-wave wireless communication may be performed.
In the millimeter-wave communication, for example, the direction of the transmission antenna is determined by transmitting a signal for determining the direction of the directivity of the transmission antenna by using the second communication unit using the communication based on any one of electric line communication, optical communication, and sound wave communication. Further, there have been proposed wireless transmission systems for performing wireless transmission between the transceivers by using the first communication unit using the electric wave of 10 GHz or more after the determination of the direction of the antenna (for example, refer to Japanese Patent Nos. 3544891 and 3333117).
Further, the method of increasing the communication distance by using the directivity of the antenna is also applied to the IEEE802.15.3c which is the standard of the wireless PAN (mmWPAN: millimeter-wave Wireless Personal Area Network) using the millimeter wave band.